The present invention relates to a control device for a hydromotor and in particular to a control device of the type having flow restricting means including a proportional directional control valve and a flow control valve with a releasable non-return valve actuated by a spring-loaded cylinder-and-piston unit.
A known control valve which is designed as a speed lowering brake valve is controlled immediately by the pump pressure which is present between the pump and the hydromotor. During fluctuating pump pressure the control piston of the brake valve, which is admitted in accordance with the fluctuations, causes the valve member of the brake valve to be controlled accordingly. Thereby, different pressures are generated between the connection connected with the brake valve and the connection of the directional control valve which is connected with the supply container, whereby at otherwise the same position of the valve member of the directional control valve, different streams of pressure medium flow from the hydromotor to the supply container (the German periodical "Fluid", February, 1979, pages 31-33).
In order to control the hydromotor independently of its load, it is also known to switch a pressure regulator valve between the control side of the brake valve and the hydromotor whose reduced constant pressure acts on the control piston of the brake valve. Thereby, the pressure at the connection point of the brake valve with the proportional directional control valve is kept constant, whereby irrespective of the pressure loss in the lines, the differential pressure between the connections of the directional control valve to the brake valve and to the supply container, is kept constant. Therefore, pressure fluctuations on the pump side or consumer side do not have any effect on the quantity of the return flow. The brake valve acts as a pressure compensator whereby its braking function is not impaired. The use of a pressure control valve is relatively expensive (DE-OS No. 29 11 891).